linux-kernel - Re: [PATCH v4] PCI: Detect and trust built-in Thunderbolt chips

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Message-ID: <CA+Y6NJE1p-nidmCZzJ7j-mJAmCLmC2q2meUf-5FFSWofWES-qA@mail.gmail.com>
Date: Wed, 28 Aug 2024 17:15:24 -0400
From: Esther Shimanovich <eshimanovich@...omium.org>
To: Lukas Wunner <lukas@...ner.de>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, Rajat Jain <rajatja@...gle.com>, 
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, Mario Limonciello <mario.limonciello@....com>, 
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>, 
	iommu@...ts.linux.dev, Mika Westerberg <mika.westerberg@...ux.intel.com>, 
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] PCI: Detect and trust built-in Thunderbolt chips

On Sun, Aug 25, 2024 at 10:49 AM Lukas Wunner <lukas@...ner.de> wrote:
>
> On Fri, Aug 23, 2024 at 04:53:16PM +0000, Esther Shimanovich wrote:
> > --- a/drivers/pci/probe.c
> > +++ b/drivers/pci/probe.c
> > +static bool pcie_has_usb4_host_interface(struct pci_dev *pdev)
> > +{
> > +     struct fwnode_handle *fwnode;
> > +
> > +     /*
> > +      * For USB4, the tunneled PCIe root or downstream ports are marked
> > +      * with the "usb4-host-interface" ACPI property, so we look for
> > +      * that first. This should cover most cases.
> > +      */
> > +     fwnode = fwnode_find_reference(dev_fwnode(&pdev->dev),
> > +                                    "usb4-host-interface", 0);
>
> This is all ACPI only, so it should either be #ifdef'ed to CONFIG_ACPI
> or moved to drivers/pci/pci-acpi.c.
>
> Alternatively, it could be moved to arch/x86/pci/ because ACPI can also
> be enabled on arm64 or riscv but the issue seems to only affect x86.

Thanks for the feedback! Adding an #ifdef to CONFIG_ACPI seems more
straightforward, but I do like the idea of not having unnecessary code
run on non-x86 systems.

I'd appreciate some guidance here. How would I move a portion of a
function into a completely different location in the kernel src?
Could you show me an example?
I'm assuming you'd want me to write another function elsewhere.
Shouldn't it be in some existing file in
`include/linux/platform_data/x86`? I don't see `arch/x86/pci/`
included anywhere.
Or would CONFIG_X86 be sufficient? (instead of or in addition to CONFIG_ACPI?)